Thanks for your advice, shadowcrono. However, it came a few minutes too soon. Cerberus is actually one of the easiest bosses in this challenge. (and no, I cannot cast dispel)

I stumbled upon one of the best strategies I've ever seen. I call it the Auto-Reflect/Dispel strategy. I had Auto-Reflect equipped on Zell and things were looking grim. Both squall and selphie were dead and cerberus had already casted triple on himself. Cerberus then used thundaga and it reflected off of Zell. Cerberus absorbed the attack, of course, but what happened was that Cerberus realized Zell had reflect, and so he became determined to get rid of it. The thing is, Auto-Reflect does not disapear when dispel is used. So cerberus begins using Dispel over and over again while I had Zell use phoenix downs. From here on out, the vast majority of Cerberus' attacks was dispel. He also used Silence a bunch, but not as much as dispel. He occasionally use his tail whip attack, but that wasnt enough to kill one party member. So I had Selphie use full-cure and squall used Darkside (500 damage. Cerberus has low vitality, apparently) until Squall had low HP. Then I pummeled him with Renzokuken while selphie did whatever she could. I had Zell use defend so that he couldn't be hurt by Cerberus' tail whip attack, which ensured that cerberus would always want to cast dispel, even if everyone else died. With this strategy Cerberus was dead in a matter of minutes.

Now I just have to battle Seifer and Edea and then I'm finished with disk 2. I also am beginning to wonder if this newfound Auto-Reflect strategy will work against other enemies. Edea is known to cast dispel, so perhaps she will occupy her time with Dispel magic.